From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761682AbZE0XsR (ORCPT ); Wed, 27 May 2009 19:48:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760020AbZE0XsG (ORCPT ); Wed, 27 May 2009 19:48:06 -0400 Received: from metis.ext.pengutronix.de ([92.198.50.35]:46295 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759689AbZE0XsF (ORCPT ); Wed, 27 May 2009 19:48:05 -0400 Date: Thu, 28 May 2009 01:48:01 +0200 From: Robert Schwebel To: Grant Likely Cc: Robert Schwebel , Timur Tabi , Janboe Ye , devicetree-discuss , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.arm.linux.org.uk, rmk@arm.linux.org.uk Subject: Re: [RFC] [PATCH] Device Tree on ARM platform Message-ID: <20090527234801.GP6805@pengutronix.de> References: <1243408083.13460.14.camel@debian-nb> <20090527150527.GK6805@pengutronix.de> <20090527162000.GM6805@pengutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: X-Sent-From: Pengutronix Entwicklungszentrum Nord - Hildesheim X-URL: http://www.pengutronix.de/ X-IRC: #ptxdist @freenode X-Accept-Language: de,en X-Accept-Content-Type: text/plain X-Impressum: Pengutronix - Linux Solutions for Science and Industry Handelsregister: Amtsgericht Hildesheim, HRA 2686 Peiner Strasse 6-8, 31137 Hildesheim, Germany Phone: +49-5121-206917-0 | Fax: +49-5121-206917-5555 Inhaber: Dipl.-Ing. Robert Schwebel X-Message-Flag: See Message Headers for Impressum X-Uptime: 01:37:45 up 90 days, 9:19, 1 user, load average: 0.74, 0.20, 0.07 User-Agent: Mutt/1.5.18 (2008-05-17) X-SA-Exim-Connect-IP: 2001:6f8:1178:2:219:66ff:fe5b:d0e3 X-SA-Exim-Mail-From: rsc@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 27, 2009 at 02:35:11PM -0600, Grant Likely wrote: > > Unfortunately, it is an incomplete data structure regarding to what > > the kernel needs. > > I don't follow your argument. It's a data structure that uniquely > describes your hardware in a way which encourages the most code reuse > possible; but is still independent of kernel internal implementation. > ie. a FDT blob should be usable not just by Linux, but also by BSD or > any of the other OS options. It is not an attempt to eliminate > platform specific code; just to reduce it as much as possible. Weird, > harry, non-standard stuff probably still needs board specific code to > handle. The oftree by design wants to be a complete hardware description. As you mention above, there are cases where you *nevertheless* need ad-hoc information about things *not* encoded into the device tree. This renders the whole concept ad absurdum. You need a machine number again - and if you need that: why not stay with the ARM model, define everything with platform data and avoid the whole thing? Regarding the multi OS argument: I consider it impossible that people agree on all micro details of a hardware decision. Will it really be possible to get a common agreement about let's say Russell's SMSC example between all these people? Remember: if we forget (or don't agree on) one single aspect which a driver developer *needs*, he will have to work around it -> machine number land. My impression is that oftree only works in a perfect world. But we don't have one, so the fundamental design decision is broken. rsc -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |